Whenever they start to smell or I can feel their coat is getting really icky. Maybe every other month or so?
Payton got a bath pretty much right after he got here, I haven't given him another yet, and he doesn't need another yet.
Auggie got a bath... uhhh... oh! The weekend before I got Payton, he got into something and we had to make him throw up, and he smelled bad because it got all over him. So a little over two months for both, and neither needs one yet.